This invention relates to a data receiving apparatus that regenerates at a receiver side a source clock frequency of a transmitter side particularly when the network clock and the source clock supplied to the transmitter side are mutually asynchronous or when the network clocks supplied to the transmitter side and the receiver side are mutually asynchronous in the communications via an ATM (Asynchronous Transfer Mode) network, a method of regenerating a source clock to be used for this, and, a computer-readable recording medium recorded with a program for making the computer execute the method according to this invention.
The ATM system collecting attention as the communication system for the multi-media era. This ATM system is characterized in that circuits between terminals are set as logical virtual circuits regardless of each medium while an STM (Synchronous Transfer Mode) system occupies a physical circuit of an STM network at each medium between terminals. Thus, the ATM system can realize an efficient multi-media communication system.
A communication system that employs the STM system will be now explained. FIG. 15 is a diagram that shows a configuration of the communication system realizing a telephone service in the STM network. A transmitter-side device group 45 transmits sound data (data string) to an STM network 47 at a constant speed. A receiver-side device group 46 receives the sound data transmitted from the STM network 47 at a constant speed. The STM network 47 communicates in a synchronous transfer mode, and outputs a network clock 42.
Telephones 40a and 40b are telephones corresponding to ISDN (Integrated Services Digital Network), and these telephones 40a and 40b are connected to PBX (Private Branch Exchanges) 41a and 41b respectively. The PBX 41a operates with a source clock 43, and the PBX 41b operates with a local clock 44. Sound information that has been input to the telephone 40a of the transmitter-side device group 45 is transmitted as sound data to the STM network 47 at a constant speed via the PBX 41a, and is then received by the telephone 10b via the PBX 41b within the receiver-side device group 46.
In the communication system of the STM system shown in FIG. 15, basically all the devices connected to the STM network 47 operate in synchronism with a sole clock frequency. In FIG. 15, a network clock 42 within the STM network 47 becomes a master clock, and the source clock 43 within the PBX 11a and the local clock 44 within the PBX 11b follow this master clock in synchronism.
Further, the sound data (data string) output from the PBX 41a is transmitted to the STM network 47 at a constant speed, for example, at 1.544 Mb/s, by using the source clock 43 within the PBX 41a as a reference. A data type transmitted at this constant speed is called CBR (Constant Bit Rate), and the sound data or the like corresponds to this CBR data, which is the data required to have real time nature.
The PBX 41b within the receiver-side device group 46 receives the sound data transmitted at a constant speed from the STM network 47, using the local clock 44 as a reference. As described above, as the source clock 43 and the local clock 44 are both slave synchronous with the network clock 42, the clock frequencies of the source clock 43 and the local clock 44 are the same as a result. Therefore, the PBX 41b can normally receive the CBR data transmitted from the PBX 41a within the transmitter-side device group 45 without over-flowing or under-flowing an inside receiving buffer not shown.
A communication system that employs the ATM system will be explained. FIG. 16 is the same as FIG. 15 but shows the configuration of a communication system realizing a telephone service in the ATM network. First, in order to realize the STM network 47 in the ATM system, that is, in order to realize by the ATM system the telephone services that are realized in a circuit switching network and a personal circuit, a service for making the ATM network appear as if it is the STM network to the transmitting and receiving devices (terminals) is necessary. That is, what is called a circuit emulation service is necessary.
In this ATM communication system, an ATM network 50 exists as a network in place of the STM network 47. A transmission CLAD (Cell Assembly and Disassembly) 51 is provided between this ATM network 50 and the transmitter-side device group 45, and a reception CLAD 52 is provided between the ATM 50 and the PBX 41b within the receiver-side device group 46. Other components are the same as those in FIG. 15. Those components that are the same as the components shown in FIG. 15 have been provided with identical legends. The above-described circuit emulation service is carried out by using the transmission CLAD 51 and the reception CLAD 52.
The ATM network 50 shown in FIG. 16 carries out communications in the asynchronous transfer mode, and transmits in an ATM cell unit that is divided into 53-byte fixed-length packets. The transmitter-side device group 45 transmits sound data to the ATM network 50 in a cell format (ATM cell) at a constant speed. The receiver-side device group 46 receives the ATM cell transmitted from the ATM network 50 at a constant speed. The ATM network 50 has network clocks 42a and 42b. The telephones 40a and 40b are ISDN telephones. The PBX""s 41a and 41b operate with the source clock 43 and the local clock 44 respectively. The transmission CLAD 51 converts a series of data string into an ATM cell, and the reception CLAD 52 converts the received ATM cell into a series of data string.
The sound information that has been input through the telephone 40a within the transmitter-side device group 45 is input as sound data (data string) to the transmission CLAD 51 via the PBX 41a, and is changed into an ATM cell in this transmission CLAD 51. Thereafter, this ATM cell is transmitted to the ATM network 50 at a constant speed. After that, the ATM cell is received by the reception CLAD 52 within the receiver-side device group 46, and this ATM cell is returned to the original data string in this reception CLAD 52, and then the data string is received by the telephone 40b via the PBX 41b. 
In this ATM communication system, devices within the ATM network 50, for example, all the devices including the ATM switching unit do not necessarily operate in synchronism with a sole frequency clock, unlike in the STM communication system. In other words, a sole frequency clock that can be commonly used is not necessarily supplied to all the devices connected to the ATM network 50. In this sense, two network clocks 42a and 42b exist within the ATM network 50 shown in FIG. 16, and the frequencies of these two network clocks 42a and 42b are not necessarily synchronous with each other.
In the mean time, in order to carry out a normal communication between the two PBX""s 41a and 41b, it is necessary to transmit and receive data at a constant speed based on the same frequency clock as a reference. For this purpose, it is necessary to post the frequency of the source clock 43 within the PBX 41a to the PBX 41b and to match the frequency of the local clock 44 within the PBX 41b with the source clock 43 by some means.
At ITU advice I.363.1 B-ISDN ATM Adaptation Layer specification: Type 1 AAL, ITU-T (Telecommunication Standardization Sector of International Telecommunication Union) defines a function that matches the frequency of the local clock with the source clock as a source clock frequency regeneration function. In other words, this is a function of regenerating at a receiver user side the source clock frequency of a transmitter user side between the transmitter user and the receiver user who are connected to each other via the ATM network.
Further, as one of the source clock frequency generation methods, the adaptive clock method has been prescribed. This adaptive clock method is used based on a pre-condition that a data transfer speed is constant (CBR) and that a range of this transfer speed is already known to the transmitter side and the receiver side. A mechanism for realizing the adaptive clock method is installed at only the receiver side. In other words, nothing is required to be installed at the transmitter side, and there is no special control information to be exchanged between the transmitter and the receiver at all.
In this case, that the range of the data transfer speed is already known to the transmitter side and the receiver side means that both the transmitter and the receiver know in advance that a data transfer speed is, for example, 1.544 Mb/sxc2x1100 ppm. Then, the receiver side calculates by using the adaptive clock method a specific value of the data transfer speed of the transmitter side, that is, the source clock frequency within the range of 1.544 Mb/sxc2x1100 ppm.
The concept of the operation of this adaptive clock method will be explained with reference to FIG. 17. A source clock regeneration buffer 23 is provided within an AAL processing section 20 to be described later for carrying out an AAL (ATM Adaptation Layer) processing in an ATM layer structure.
At the receiver side, reception cells 60a to 60c are written sequentially into the source clock regeneration buffer 23, and a buffering is carried out to a read starting threshold value TH that is a center value (xc2xd) of the total capacity of the source clock regeneration buffer 23. Thereafter, the reception cells 60a to 60c are read out sequentially from the source clock regeneration buffer 23 by using the local clock 44. According to the adaptive clock method, control information for controlling the frequency of the local clock 44 is calculated based on a buffer remaining volume within the source clock regeneration buffer 23.
When the empty space in the buffer (hereafter, buffer remaining volume) is in an increasing trend, the frequency of the local clock 44 is considered to be lower than the source clock 43. Therefore, the frequency of the local clock 44 is controlled to be increased. On the other hand, when the buffer remaining volume is in a decreasing trend, the frequency of the local clock 44 is controlled to be decreased. In the ITU-T advice, only the above operation concept of the Adaptive clock method is indicated, and almost nothing is described about a detailed specification for realizing this method and a method of calculating this control information.
A conventional data receiving apparatus having a source clock frequency generation function and the Adaptive clock method will be explained here. FIG. 18 is a block diagram showing a detailed structure of the reception CLAD 52 having the source clock frequency generation function. In this reception CLAD 52, a physical layer processing section 18 processes a physical layer in an ATM layer structure. An ATM layer processing section 19 carries out an ATM layer processing in the ATM layer structure. An AAL processing section 20 carries out an AAL processing in the ATM layer structure. An STM processing section 21 carries out an STM interface finish processing in an STM. A device managing section 22 carries out an overall device management of the reception CLAD 52.
FIG. 19 is a block diagram showing a detailed structure of the AAL processing section 20. In this AAL processing section 20, a source clock regeneration buffer 23 temporarily holds a reception cell. A source clock regenerating section regenerates the source clock. A buffer control section 11 controls the reading from the source clock regeneration buffer 23. A buffer-remaining volume monitoring section 12 obtains a buffer remaining volume H from a write signal and a read signal to the source clock regeneration buffer 23, and monitors this buffer remaining volume H. A control-voltage calculating section 1 calculates a control voltage V to a voltage control crystal oscillator 13 to be described later based on the buffer remaining volume H output from the buffer-remaining volume monitoring section 12. The voltage control crystal oscillator (VCXO) 13 changes an oscillation frequency (local clock 44) according to the control voltage V from the control-voltage calculating section 1.
FIG. 20 is a block diagram showing a detailed structure of the control-voltage calculating section 1. In this control-voltage calculating section 1, an operating section 2 calculates a control value U from the buffer remaining volume H that is output from the buffer-remaining volume monitoring section 12. A D/A converter 3 converts the control value U that is a digital value output from the operating section 2 into a control voltage V that is an analog value. A timer 4 instructs the operating section 2 to execute the operation at each constant cycle.
The device managing section 22 shown in FIG. 18 manages the overall devices in the reception CLAD 52, and sets various parameters to and collects statuses from the physical layer processing section 18, the ATM layer processing section 19, the AAL processing section 20, and each section 18 to 21 of the STM processing section 21 respectively. In order to realize this function, the device managing section 22 and each of the sections 18 to 21 are connected by a control bus.
Further, in order to set various parameters and to collect statuses as described above, this control bus is also connected to sub-blocks not shown within each of the sections 18 to 21, such as, for example, sub-blocks within the AAL processing section 20. A data bus width at an ATM interface and an STM interface is serial (1 bit) respectively, but data is transmitted and received generally in the width of 8 bits within each of the sections 18 to 21.
For example, when the ATM interface speed is 155.52 MHz, the STM interface speed, that is a source clock frequency, is 1.544 MHz, and its variation range is xc2x1100 ppm, an interface is carried out in the 8-bit width within the reception CLAD 52 as described above. As most of them operate in the clock of the ATM interface system, the inside reference clock becomes 19.44 MHz (=155.52 MHz/8 bits).
Referring now to FIG. 16, the sound data that has been output from the telephone 40a within the transmitter-side device group 45 is input to the transmission CLAD 51 via the PBX 41a, and is converted in to an ATM cell here, and is thereafter transmitted to the ATM network 50 at a constant speed. Thereafter, the ATM cell is transmitted to the receiver-side device group 46 from the ATM network 50 at a constant speed.
The ATM cell that has been transmitted from the ATM network 50 to the receiver-side device group 46 is received by the reception CLAD 52. In other words, as shown in FIG. 18, the ATM cell is input to the physical layer processing section 18 via the ATM interface. This physical layer processing section 18 carries out a physical layer processing of SDH (Synchronous Digital Hierarchy)/SONET (Synchronous Optical Network), and cell synchronization, and a serial/parallel (8-bit) conversion.
The data processed by the physical layer processing section 18 is sent to the ATM layer processing section 19. The ATM layer processing section 19 carries out an ATM layer processing such as a filtering based on VPI (Virtual Path Identifier)/VCI (Virtual Channel Identifier), and then delivers the data to the AAL processing section 20.
In general, the CBR data such as the sound data is transmitted by utilizing an AAL type 1. Therefore, the AAL processing section 20 carries out the AAL type 1 processing such as a cell abandon/erroneous insertion check processing, a fluctuation absorption processing, a conversion from an ATM cell to a data string, and a source clock frequency regeneration processing, according to a sequence number within the header of the AAL type 1. In this AAL processing, the frequency of the source clock 43 as the STM interface clock is regenerated.
The sound data that has been converted into the data string by the AAL processing section 20 is further sent to the STM processing section 21. The data string is then subjected to an STM interface finishing processing such as an STM frame generation, and a parallel (8-bit) /serial conversion by the STM processing section 21. Thereafter, the data string is transmitted to the PBX 41b via the STM interface. Next, details of the source clock frequency regeneration operation in the AAL processing section 20 will be explained.
First, within the AAL processing section 20, reception cells 60a to 60c that have been input from the ATM layer processing section 19 are written into a source clock regeneration buffer 23 based on a write signal. In this case, sound data of an effective speed 1.544 Mb/s is transferred between blocks at a data transfer speed of 155.52 Mb/s. Therefore, the transfer state of the reception cells 60a to 60c at this time becomes in a burst shape in a cell unit as shown in FIG. 3(a). The buffer-remaining volume monitoring section 12 monitors a write signal from the ATM layer processing section 19, and monitors that the sound data is buffered to the read starting threshold value TH that is set to the center value (xc2xd) of the total capacity of the source clock regeneration buffer 23.
When the buffer-remaining volume monitoring section 12 has detected that the sound data has been buffered to the read starting threshold value TH, the buffer-remaining volume monitoring section 12 gives a start instruction S to the buffer control section 11 to start the reading from the source clock regeneration buffer 23, and at the same time instructs the control-voltage calculating section 1 to start the operation. Thereafter, the operating section 2 within the control-voltage calculating section 1 calculates the control value U based on the buffer remaining volume H sent from the buffer-remaining volume monitoring section 12, according to the operation execution instruction sent from the timer 4 at a constant cycle. The buffer-remaining volume monitoring section 12 thereafter continuously obtains the buffer remaining volume H from the operation of the write signal and the read signal, and posts this buffer remaining volume H to the control-voltage calculating section 1.
As the reading from the source clock regeneration buffer 23 is carried out at the effective speed of the sound data 1.544 Mb/s, the transfer state of the reception cells 60a to 60c becomes in a continuous data string as shown in FIG. 3(b). The difference in the lengths of the reception cells 60a to 60c between those shown in FIG. 3(a) and those shown in FIG. 3(b) is due to the difference in data transfer speeds between the two cases. The data sizes for these are all the same.
When the buffer remaining volume H is in the increasing trend, the control-voltage calculating section 1 regards the frequency of the local clock 44 to be lower than the source clock 43, and controls the voltage control crystal oscillator 13 to increase the frequency of the local clock 44. On the other hand, when the buffer remaining volume H is in the decreasing trend, the control-voltage calculating section 1 controls to lower the frequency of the local clock 44. The voltage control crystal oscillator 13 changes the oscillation frequency of the local clock 44 according to the control voltage V from the control-voltage calculating section 1. The buffer control section 11 outputs a read signal to the source clock regeneration buffer 23 based on the local clock 44 output from the voltage control crystal oscillator 13.
Referring now to FIG. 20, in the control-voltage calculating section 1, the operating section 2 calculates the control value U from the buffer remaining volume H according to the operation execution instruction from the timer 4, and posts this control value U to the D/A converter 3. An equation used for obtaining the control value U in the operation section 2 is, for example, as follows:
Control value U=sensitivity Axc3x97(weighted average value M of (buffer remaining volume Hxe2x88x92center value C))+offset value Bxe2x80x83xe2x80x83(1)
In this case, sensitivity A is a coefficient for converting the weighted average value M into the control value U. When this value is larger, the oscillation frequency of the local clock 44 comes to react sensitively to changes in the weighted average value M, and the convergence time also becomes shorter. The offset value B is a value for outputting the reference frequency to the voltage control crystal oscillator 13. For example, when the frequency variable range is 1.544 MHzxc2x1100 ppm, this is a value for outputting 1.544 MHzxc2x1100 ppm that is the center frequency thereof. Further, the center value C means the center value (xc2xd) of the total capacity of the source clock regeneration buffer 23, and this is the same value as the read starting threshold value TH.
The buffer remaining volume H is not limited to a buffer remaining volume displayed in a detailed number of bytes or number of bits, but may also be a value displayed in any optional unit such as 48 bytes and 64 bytes. For example, 64 bytes may be used as a minimum unit.
The control value U as a digital value calculated by through equation (1) is converted into the control voltage V as an analog value by the D/A converter 3, and a result is used for increasing or decreasing the frequency of the local clock 44 that is the output of the voltage control crystal oscillator 13.
The outline of the above-described source clock frequency generation operation is summarized as follows for easy understanding.
(1) When the weighted average value M is 0, the reference frequency (xc2x10 ppm) is output.
(2) When the weighted average value M is larger (plus) than 0, a frequency higher than the reference frequency is output.
(3) When the weighted average value M is much larger than 0, a higher frequency is output.
(4) When the weighted average value M is smaller (minus) than 0, a frequency lower than the reference frequency is output.
(5) When the weighted average value M is much lower than 0, a lower frequency is output.
The local clock 44 that is frequency-synchronized with the source clock 43 is output from the voltage control crystal oscillator 13 based on the source clock frequency generation operation. The buffer control section 11 outputs the read signal to the source clock regeneration buffer 23 based on the local clock 44, and the ATM cell is read from the source clock regeneration buffer 23 based on this read signal.
Japanese Patent Application Laid-open No. 10-271115, discloses a method of realizing the adaptive clock method in detail. A smoothing buffer is proved at a pre-stage of the source clock regeneration buffer to suppress a sudden variation in the buffer remaining volume of the source clock regeneration buffer, thereby to stabilize the regeneration clock frequency.
Japanese Patent Application Laid-open No. 9-247156 also discloses a method of realizing the adaptive clock method. A regeneration clock frequency is calculated from the buffer remaining volume of the source clock regeneration buffer.
Japanese Patent Application Laid-open No. 7-46275 also discloses a method of realizing the adaptive clock method. A change volume in a deviation of the buffer remaining volume is monitored, and a regeneration clock frequency is calculated using a program of a microprocessor based on a result of this monitoring, thereby open-loop controlling the regeneration clock frequency.
The local clock 44 at the receiver side, that is the convergence time of the regeneration clock, and the frequency stability after the convergence in the above-described conventional ATM communication system are in an inversely proportional (tradeoff) relationship. In other words, as the sensitivity A in equation (1) is made larger, the oscillation frequency of the regeneration clock reacts sensitively to the change in the average value M. As a result, the convergence time becomes short, but at the same time, the oscillation frequency also reacts sensitively to the noise component such the arrival fluctuation of reception cells and a variation in the buffer remaining volume H due to the burst writing of the reception cells into the source clock regeneration buffer 23. Therefore, the frequency stability after the convergence is aggravated. On the other hand, when the sensitivity A in equation (1) is made smaller, the noise component becomes dull, and the frequency stability after the convergence is improved. However, the convergence time becomes longer.
Thus, there has been a problem in the conventional source clock regeneration method that, either the shortening of the convergence time or the frequency stability after the convergence has to be sacrificed.
FIG. 21 shows a detailed example of a state of change in the regeneration clock frequency in relation to a lapse time after starting the clock regeneration operation when the source clock frequency is 1.544 MHz+50 ppm and the initial value of the regeneration clock frequency is 1.544 MHzxc2x10 ppm. Convergence curves 70a to 70c show representative convergence curves when the sensitivity A in equation (1) is the same and constant, and the average modulus N that shows the total number of the buffer remaining volume H used for calculating the weighted average value M and the value of the detection interval T of the buffer remaining volume H have been changed respectively. Among these convergence curves 70a to 70c, the convergence curve 70b is the most ideal convergence curve, with the shortest convergence time as well. The convergence curve 70a shows a case where the average modulus N or the detection interval T is larger than the convergence curve 70b. On the other hand, the convergence curve 70c shows a case where the average modulus N or the detection interval T is smaller than the convergence curve 70b. In both cases, the convergence time is slow.
A combination of the sensitivity A, the average modulus N and the detection interval T that makes it possible to obtain the ideal convergence curve shown in the convergence curve 70b, that is an optimum solution, exists by a plurality of sets in one system. However, in each of these optimum solutions existing by a plurality of sets, the sensitivity A, the average modulus N and the detection interval T are mutually in an inversely proportional relationship. When two values out of these three values have been determined, the remaining one value is also uniquely determined. This is expressed by the following expressing (2).
Sensitivity Axc3x97average modulus Nxc3x97detection interval T=constantxe2x80x83xe2x80x83(2)
The convergence time of the optimum solution basically depends on only the value of the sensitivity A.
The weighted average calculation has a work as a low-pass filter that removes the noise component of the higher harmonics and suppresses unnecessary variations in the regenerated clock frequency. Further, as the average modulus N is made larger, that is, as the weight of the latest buffer remaining volume H is made smaller, the cutoff frequency of the low-pass filter becomes smaller, thereby improving the frequency stability after the convergence.
As a result, in order to shorten the convergence time of the regeneration clock frequency and further to improve the frequency stability after the convergence, it can be known that both the sensitivity A and the average modulus N may be made as large values as possible.
However, when the average modulus N is made larger, the scale of the operating circuit of the control value U (operating volume in the case of operating by software) also becomes larger. Further, as long as the constraint (constraint to obtain an optimum solution) shown in equation (2) holds, the detection interval T needs to be made smaller when the sensitivity T and the average modulus N are made larger. This also results in an increase in the operation speed of the operating circuit (frequency of operation in the case of operating by software) Usually, there is an upper limit to the scale and operation speed of the operating circuit that can be actually realized. Therefore, there is a case where it is not possible to obtain a circuit that can satisfy both a required convergence time and required frequency stability, due to this limit.
Therefore, when the scale of the operating circuit and the operation speed of the operating circuit are additionally taken into account, the above-described conventional source clock regeneration method has had a problem that any one of the convergence time, the frequency stability after the convergence, the scale of the operating circuit, and the operation speed of the operating circuit has to be sacrificed.
Further, although the transmission interval of the transmission cells transmitted from the transmission CLAD 51 to the ATM network 50 is constant, the reception intervals of reception cells that are received by the reception CLAD 52 or the source clock regeneration buffer 23 is not constant and has a high possibility of being fluctuated due to the variation in the transfer delay within the ATM network 50. In order to normally convert the ATM cells into a data string in the reception CLAD 52, it is necessary to absorb this delay fluctuation of the reception cell by some means. As one method of realizing this, there is considered a method of making the source clock regeneration buffer 23 bear a function as a fluctuation absorption buffer. In this case, the fluctuation proof of the data receiving apparatus basically depends on the capacity of the source clock regeneration buffer 23.
The fluctuation proof strictly becomes one of a smaller value of the xe2x80x9cbuffer remaining volumexe2x80x9d and the xe2x80x9ctotal capacity of the source clock regeneration buffer 23xe2x88x92buffer remaining volumexe2x80x9d. In other words, the fluctuation proof becomes a maximum when the buffer remaining volume is equal to the center value (xc2xd) of the total capacity of the source clock regeneration buffer 23. When the buffer remaining volume is deviated from the center value, the fluctuation proof is lower, or an overflow or an underflow occurs easily. However, as shown in equation (1), according to the conventional source clock regeneration method, the oscillation frequency of the regeneration clock is controlled using the weighted average value M of the xe2x80x9cdeviation from the center value of the buffer remaining volumexe2x80x9d. Therefore, the conventional source clock regeneration method has had a problem that as the source clock frequency is farther from the reference frequency, the weighted average value M becomes farther from 0. In other words, the center of the variation of the buffer remaining volume becomes farther from the center value, which results in the lowering of the fluctuation proof.
Therefore, it is an object of the present invention to obtain a data receiving apparatus that can reduce a convergence time of a regeneration clock, that can increase the frequency stability after a convergence, and that can suppress the influence of the source clock frequency given to the fluctuation proof to a minimum, under a limit to the scale of the operating circuit or to the operation speed of the operating circuit, a method of regenerating a source clock to be used therefor, and a computer-readable recording medium recorded with a program for making a computer execute this method.
A data receiving apparatus relating to this invention is characterized in that it comprises a buffer unit for holding data that has been transmitted from a data transmitting apparatus to a transfer network at a constant speed based on a source clock, and that is then received from the transfer network at a constant speed; and a source clock regenerating unit for detecting a buffer remaining volume that is a data volume held by the buffer unit, and for regenerating the source clock according to this buffer remaining volume. The source clock regenerating unit comprises an operating unit for taking a weighted average value of a plurality of buffer remaining volumes that have been sequentially detected, multiplying a predetermined sensitivity coefficient to this weighted average value, and further adding a predetermined offset value, thereby to obtain a control value for regenerating the source clock; and a control unit for setting a regeneration clock to a manipulated variable to be used for calculating the control value capable of converging to the source clock at a high speed during a period from when a source clock regeneration operation has started till when the regeneration clock satisfies a predetermined condition for coming closer to the source clock frequency, and for setting the regeneration clock to the manipulated variable capable of stably regenerating the source clock after this predetermined condition has been satisfied.
According to this invention, the operating unit takes a weighted average value of the plurality of buffer remaining volumes sequentially detected, and multiplies a predetermined sensitivity coefficient to this weighted average value, and further adds a predetermined offset value, thereby to obtain a control value for regenerating the source clock. In this case, the control unit sets a regeneration clock to a manipulated variable to be used for calculating the control value capable of converging to the source clock at a high speed during a period from when a source clock regeneration operation has started till when the regeneration clock satisfies a predetermined condition for coming closer to the source clock frequency, and sets the regeneration clock to the manipulated variable capable of stably regenerating the source clock after this predetermined condition has been satisfied, thereby regenerating the source clock.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit has a timer for counting a pre-decided duration of time (hereafter, constant time), and the predetermined condition is a lapse of the constant time counted by the timer. According to this invention, a high-speed convergence to the source clock frequency is carried out until when a constant time counted by the timer has passed, and a clock regeneration control of high frequency stability is carried out by the lapse of this constant time.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit has a time measuring unit for counting a frequency variation range of the regeneration clock, and the predetermined condition is that the frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value. According to this invention, a high-speed convergence to the source clock frequency is carried out until when the frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value. A clock regeneration control of high frequency stability is carried out when the frequency variation range of the regeneration clock has become equal to or lower than the predetermined value.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit has a timer for counting a constant time and a time measuring unit for counting a frequency variation range of the regeneration clock, and the predetermined condition is to satisfy one of that the constant time counted by the timer has lapsed and that the frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value. According to this invention, a highspeed convergence to the source clock frequency is carried out until when one of the conditions that a constant time passes and that the frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value is satisfied. A clock regeneration control of high frequency stability is carried out after one of the conditions has been satisfied.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit sets the sensitivity coefficient to a small value and at the same time further adds a predetermined correction value to the offset value, after the predetermined condition has been satisfied. According to this invention, before satisfying the predetermined condition, the sensitivity coefficient is set large so that the convergence time becomes short. After the predetermined condition has been satisfied, the sensitivity coefficient is set small, and at the same time a predetermined correction value is further added to the offset value, thereby carrying out a source clock regeneration control of high frequency stability.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit sets small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied. According to this invention, the weight of the buffer remaining volume at the latest side is set small from out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit changes a predetermined interval for detecting the buffer remaining volume, after the predetermined condition has been satisfied. According to this invention, a predetermined interval for detecting the buffer remaining volume is changed, after the predetermined condition has been satisfied.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit further adds a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied. According to this invention, a predetermined correction value is further added to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the correction value is a time threshold value that changes along with a lapse of time toward a final value after the final value has been decided. According to this invention, the correction value is a time threshold value that changes along with a lapse of time toward a final value after the final value has been decided.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit sets a multiplication value of the sensitivity coefficient, an average modulus for prescribing the weighted average calculation of the plurality of buffer remaining volumes, and the predetermined interval, to a constant value corresponding to an optimum value. According to this invention, a multiplication value of the sensitivity coefficient, the average modulus, and the predetermined interval is set to a constant value corresponding to an optimum value.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit carries out a plurality of processing in combination from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, the processing of changing a predetermined interval for detecting the buffer remaining volume, and the processing of further adding a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied.
According to this invention, the control unit carries out a plurality of processing in combination from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, the processing of changing a predetermined interval for detecting the buffer remaining volume, and the processing of further adding a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the control unit adds a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied, and carries out one or more processing in combination from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, and the processing of changing a predetermined interval for detecting the buffer remaining volume, after the predetermined condition has been satisfied.
According to this invention, the control unit adds a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, after the predetermined condition has been satisfied, and carries out one or more processing in combination from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, and the processing of changing a predetermined interval for detecting the buffer remaining volume, after the predetermined condition has been satisfied.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, when the frequency variation range of the regeneration clock has exceeded a predetermined value, the control unit returns the regeneration clock to an initial set state of before starting the source clock regeneration operation, sets the regeneration clock to a manipulated variable to be used for calculating the control value capable of converging the source clock at a high speed during a period from this initial set state till when the regeneration clock satisfies a predetermined condition for coming closer to the source clock frequency, and sets the regeneration clock to the manipulated variable capable of stably regenerating the source clock after this predetermined condition has been satisfied.
According to this invention, when the frequency variation range of the regeneration clock has exceeded a predetermined value, the control unit returns the regeneration clock to an initial set state before starting the source clock regeneration operation, sets the regeneration clock to a manipulated variable to be used for calculating the control value capable of converging the source clock at a high speed during a period from this initial set state till when a regeneration clock satisfies a predetermined condition for coming closer to the source clock frequency, and sets the regeneration clock to the manipulated variable capable of stably regenerating the source clock after this predetermined condition has been satisfied.
A data receiving apparatus relating to the next invention is characterized in that, in the above invention, the data receiving apparatus further comprises a setting unit for setting the contents of the setting control that the control unit carries out. According to this invention, it is possible to set the contents of the setting control that the control unit carries out, by using the setting unit.
A source clock regeneration method relating to the next invention is characterized in that, the source clock regeneration method is for holding data that has been transmitted from a data transmitting apparatus to a transfer network at a constant speed based on a source clock and the data received from the transfer network at a constant speed, for detecting a buffer remaining volume that is a data volume held by the buffer unit, and for regenerating the source clock according to this buffer remaining volume. The source clock regeneration method comprises a first step of taking a weighted average of a plurality of buffer remaining volumes sequentially detected during a period from when a source clock regeneration operation has been stated till when a regeneration clock has satisfied a predetermined condition for coming closer to the source clock, multiplying a predetermined coefficient to this weighted average value, further adding a predetermined offset value thereby to obtain a control value for regenerating the source clock, outputting the calculated control value and converging the frequency of the regeneration clock to the source clock at a high speed; and a second step of change setting a manipulated variable to be used for the calculation of the control value after satisfying the predetermined condition, and stably controlling the regeneration of the frequency of the regeneration clock.
According to this invention, first, a weighted average of a plurality of buffer remaining volumes sequentially detected is taken during a period from when a source clock regeneration operation has been stated till when a regeneration clock has satisfied a predetermined condition for coming closer to the source clock, then a predetermined coefficient is multiplied to this weighted average value, further a predetermined offset value is added thereby to obtain a control value for regenerating the source clock, the calculated control value is output and the frequency of the regeneration clock is converged to the source clock at a high speed, and next, a manipulated variable to be used for the calculation of the control value is changed after satisfying the predetermined condition, and the regeneration of the frequency of the regeneration clock is stably controlled.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the predetermined condition is a lapse of a constant time after the source clock regeneration operation has been started. According to this invention, a high-speed convergence to the source clock frequency is carried out until when a constant time counted by the timer has passed, and a clock regeneration control of high frequency stability is carried out by the lapse of this constant time.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the predetermined condition is that a frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value. According to this invention, a highspeed convergence to the source clock frequency is carried out until when the frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value. A clock regeneration control of high frequency stability is carried out when the frequency variation range of the regeneration clock has become equal to or lower than the predetermined value.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the predetermined condition is to satisfy one of that a constant time has passed after the source clock regeneration operation has been started and that a frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value. According to this invention, a high-speed convergence to the source clock frequency is carried out until when one of the conditions that a constant time passes and that the frequency variation range of the regeneration clock becomes equal to or lower than a predetermined value is satisfied. A clock regeneration control of high frequency stability is carried out after one of the conditions has been satisfied.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the change setting of the manipulated volume at the second step is setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value. According to this invention, the change setting of the manipulated volume at the second step is setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the change setting of the manipulated volume at the second step is setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value. According to this invention, the change setting of the manipulated volume at the second step is setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the change setting of the manipulated volume at the second step is changing a predetermined interval for detecting the buffer remaining volume. According to this invention, the change setting of the manipulated volume at the second step is changing a predetermined interval for detecting the buffer remaining volume.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the change setting of the manipulated volume at the second step is further adding a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value. According to this invention, the change setting of the manipulated volume at the second step is further adding a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the correction value is a time threshold value that changes along with a lapse of time toward a final value after the final value has been decided. According to this invention, the correction value is a time threshold value that changes along with a lapse of time toward a final value after the final value has been decided.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the manipulation volume sets a multiplication value of the sensitivity coefficient, an average modulus for prescribing the weighted average calculation of the plurality of buffer remaining volumes, and the predetermined interval, to a constant value corresponding to an optimum value. According to this invention, the manipulation volume sets a multiplication value of the sensitivity coefficient, an average modulus for prescribing the weighted average calculation of the plurality of buffer remaining volumes, and the predetermined interval, to a constant value corresponding to an optimum value.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the second step is the process of carrying out two or more processing in combination from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, the processing of changing a predetermined interval for detecting the buffer remaining volume, and the processing of further adding a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value.
According to this invention, the second step is the process of carrying out two or more processing in combination a from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, the processing of changing a predetermined interval for detecting the buffer remaining volume, and the processing of further adding a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the second step further adds a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, and further includes a third step of carrying out one or more processing in combination from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, and the processing of changing a predetermined interval for detecting the buffer remaining volume, after the predetermined condition has been satisfied again.
According to this invention, the second step further adds a predetermined correction value to the buffer remaining volume of the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, and the source clock regeneration method further comprises a third step of carrying out one or more processing in combination from out of the processing of setting the sensitivity coefficient to a small value and at the same time further adding a predetermined correction value to the offset value, the processing of setting small the weight of the buffer remaining volume at the latest side out of the plurality of buffer remaining volumes used for the calculation of the weighted average value, and the processing of changing a predetermined interval for detecting the buffer remaining volume, after the predetermined condition has been satisfied again.
A source clock regeneration method relating to the next invention is characterized in that, in the above invention, the source clock regeneration method further comprises a fourth step of returning a regeneration clock to an initial set state of before starting the source clock regeneration operation when the frequency variation range of the regeneration clock has exceeded a predetermined value after the predetermined condition has been satisfied, and thereafter further sequentially carries out the first step, the second step or the third step. According to this invention, a regeneration clock is returned to an initial set state of before starting the source clock regeneration operation when the frequency variation range of the regeneration clock has exceeded a predetermined value after the predetermined condition has been satisfied, and thereafter further the first step, the second step or the third step is sequentially carried out.
A recording medium relating to the next invention is characterized in that the recording medium is recorded with a program for making a computer execute one of the methods described in the above-described inventions. Based on this arrangement, this program can be read by a machine so that computers can realize the above-described operations of the inventions.